The invention relates to a method and a device for separating wound tubes and/or cutting them to length.
Metal tubes are called wound tubes, which are formed by windings comprising a metal strip, which windings are connected to each other relatively loosely in a form-fitting fashion. Typical forms of the connection are hooked profiles (so-called LIH-liners) and crimped profiles (Agrafe-profile, so-called LIS-liner).
Wound tubes with hooked profiles are characterized in a particularly high flexibility. Wound tubes with crimped profiles are relatively stiff overall. Based on the high flexibility particularly wound tubes with a hooked profile are hard to weld, because here no defined welding geometry develops.
A particularly preferred application of the above-mentioned wound tubes is the gas conduction in the exhaust field of passenger vehicles and utility vehicles. Additional applications are e.g., protective tubes for fiberglass, telephone lines, lines of measuring devices, or alarm systems.
A particular problem is given in wound tubes in the fact that they may also unwind after being cut to length. Then their assembly is no longer possible or only possible with increased expenses, which is undesired in production.
According to prior art, the above-mentioned wound tubes are cut, e.g., using a melting cut-off saw, and subsequently the loose end is fixed via a manually placed welding spot. This is work-intensive and accordingly costly and therefore less suitable for serial production. In addition, there is the fact that particles are undesired when wound tubes are used in exhaust systems, here particles are undesired, which may however develop when cutting a wound tube with a mechanical saw. Such particles or chips can destroy filters or other downstream arranged components, particularly components for cleaning exhaust gas. Therefore, increasingly laser cutting methods are used.
For this purpose, three axially off-set laser beams are used, guided circumferentially around the tube. A first and a second beam each place a circumferential seam for fixing the material of the wound tube, with the two seams being arranged axially off-set in reference to each other.
Subsequently, the wound tube is severed between the two seams via a third laser beam. Here it has proven disadvantageous that the two seams are embodied in a relatively undefined fashion in case of wound tubes, because a wound tube exhibits, based on its general design as described above, only relatively little material and a relatively large clear space located therebetween. Here the risk is given that during the attempt of forming a laser welding seam the wound tube is here rather severed than fixed.
Additionally, in the above-mentioned method relatively large tolerances develop due to the inherent mobility of the wound tube. In the past, this has resulted in the fact that during the actual severing process via the third laser beam the previously generated seams themselves were damaged as well. Here, repeatedly an unwinding of the wound tube occurs so that the assembly is at least aggravated.